PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD 300 PM EDT THU AUGUST 21 2003 . . . . . . . . SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS THE SEASONAL OUTLOOK REFLECTS THE PRESENCE OF LONG TERM TRENDS ON U.S. TEMPERATURE AND PRECIPITATION...STATISTICAL FORECAST TOOLS ...WITH SOME INPUT FROM NUMERICAL MODELS DURING THE FIRST SEVERAL SEASONS AND - FINALLY - THE LIKELY CONTINUATION OF ENSO NEUTRAL CONDITIONS IN THE TROPICAL PACIFIC DURING THE NEXT SEVERAL MONTHS. THE RAPID COOLING - TREND TOWARDS LA NINA - IN THE EQUATORIAL PACIFIC DURING JANUARY THROUGH MAY WAS FOLLOWED BY WARMING DURING JUNE AND EARLY JULY. BY MID-AUGUST SURFACE AND SUBSURFACE TEMPERATURES IN THE EQUATORIAL PACIFIC WERE NEAR THEIR LONG TERM AVERAGES EXCEPT FOR THE FAR WESTERN (EASTERN) SECTIONS WERE POSITIVE (NEGATIVE) DEPARTURES FROM AVERAGE PERSISTED. THE LACK ON ANY SIGNIFICANT TREND TOWARDS EITHER LA NINA OR EL NINO INCREASES THE UNCERTAINTY ASSOCIATED WITH THIS SET OF FORECASTS. THEREFORE - EXCEPT FOR AREAS WITH STRONG TRENDS - BOTH PROBABILITIES AND AREA COVERED BY NON-EC PROBABILITIES WILL BE RELATIVELY LOW IN THIS SET OF FORECASTS. THE FORECASTS FOR ALL SEASONS WERE BASED ON A CONTINUATION OF ENSO-NEUTRAL CONDITIONS AND - THEREFORE - PRIMARILY REFLECT LONG TERM TRENDS. THE OUTLOOK FOR SEPTEMBER THROUGH NOVEMBER 2003 CALLS FOR ABOVE NORMAL TEMPERATURES OVER THE SOUTHWEST AND EXTREME SOUTHERN FLORIDA. SON PRECIPITATION IS EXPECTED TO BE BELOW AVERAGE OVER CALIFORNIA - NEVADA - UTAH AND ARIZONA AND ABOVE AVERAGE OVER PORTIONS OF THE SOUTHEAST. . . . . . . . . BASIS AND SUMMARY OF THE CURRENT LONG-LEAD OUTLOOK NOTE: FOR GRAPHICAL DISPLAYS OF THE FORECAST TOOLS DISCUSSED BELOW SEE: http://www.cpc.ncep.noaa.gov/products/predictions/90day/tools/briefing CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS EASTERLY WINDS - WHICH WERE STRONGER THAN AVERAGE OVER THE CENTRAL AND WEST- CENTRAL EQUATORICAL PACIFIC DURING MARCH AND APRIL - SUBSEQUENTLY GAVE WAY TO MODEST WESTERLY ANOMALIES OVER MUCH OF THE PACIFIC IN LATE MAY - EARLY JUNE. THE EQUATORIAL EASTERLIES THEN STRENGTHENED OVER THE CENTRAL PACIFIC DURING LATE JUNE-EARLY JULY - WITH NEAR AVERAGE OR SLIGHTLY STRONGER THAN AVERAGE EASTERLIES PREVAILING THROUGH MID-AUGUST. THE TRADITIONAL TAHITI-MINUS-DARWIN- BASED SOI ROSE TO +0.2 IN JULY - THE FIRST POSITIVE VALUE OF THIS INDEX SINCE EARLY 2002. BY MID-AUGUST POSITIVE EQUATORIAL SST DEPARTURES - GREATER THAN +0.5C - WERE OBSERVED BETWEEN 160E AND 165W. THE REMAINDER OF THE EQUATORIAL PACIFIC - BETWEEN 165W AND THE SOUTH AMERICAN COAST - FEATURED NEAR AVERAGE SST. SUB-SURFACE WATER TEMPERATURES INCREASED DURING JUNE AND JULY IN RESPONSE TO A KELVIN WAVE INITIATED BY THE WESTERLY WIND ANOMALIES IN LATE MAY - EARLY JUNE. RECENTLY - SUBSURFACE TEMPERATURES HAVE COOLED AND BY MID-AUGUST WERE CLOSE TO AVERAGE THROUGHOUT THE EQUATORIAL PACIFIC. THUS THE UPPER OCEAN HEAT CONTENT IS ALSO NEAR AVERAGE - WHICH INDICATES THE LIKELIHOOD THAT ENSO-NEUTRAL CONDITIONS WILL CONTINUE FOR THE NEXT SEVERAL MONTHS. . . . . . . . . PROGNOSTIC DISCUSSION OF SST FORECASTS FORECASTS FROM MULTIPLE MODELS GIVE A RANGE OF POSSIBLE FUTURE SST PATTERNS IN THE TROPICAL PACIFIC - INDICATING CONSIDERABLE UNCERTAINTY - ALTHOUGH MOST PROJECTIONS FALL WITHIN THE ENSO-NEUTRAL RANGE - NINO 3.4 SST ANOMALY WITHIN THE RANGE OF -0.5C TO +0.5C. TO SEE THESE FORECASTS GO TO: http://www.cpc.ncep.noaa.gov/products/predictions/90day/tools/briefing/plume.gif A CONSOLIDATION FORECAST OF IN-HOUSE TOOLS INDICATES THAT NINO 3.4 SST ANOMALIES WILL REMAIN NEAR ZERO THROUGH SPRING 2004. THEREAFTER - NINO 3.4 SST ANOMALIES ARE PREDICTED TO SLOWLY INCREASE - BUT REMAIN LESS THAN +0.5C - THROUGH SUMMER 2004. CONFIDENCE IN THE FORECAST IS RELATIVELY HIGH THROUGH FALL 2003 AND DECREASES THEREAFTER. SSTA FORECASTS FOR THE NINO 3.4 REGION BY MODELS RUN IN OTHER CENTERS GENERALLY FALL IN THE RANGE BETWEEN -0.5C AND +0.5C OR ENSO-NEUTRAL. PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOK THE STATISTICAL TOOLS - CCA - OCN - SMLR - WERE CONSULTED AT ALL LEAD TIMES. DYNAMICAL MODEL FORECASTS FROM NCEP AND OTHER FORECAST CENTERS WERE EXAMINED FOR THE PERIOD SON 2003 - DJF 2003-2004. IN SON WE ALSO LOOKED AT THE SOIL MOISTURE TOOL CAS. INITIAL SOIL MOISTURE ANOMALIES CONTINUE TO BE UNUSUALLY WET IN THE SOUTHEAST AND THE MIDDLE ATLANTIC STATES AND DRY IN SECTIONS OF THE CENTRAL GREAT PLAINS - THE SOUTHWEST AND THE ROCKIES. CAS AND OCN TEMPERATURE FORECASTS WERE CONSIDERED TOGETHER AS A CONSOLIDATION OF THESE TWO TOOLS AND WERE USED FOR THOSE AREAS AND PROJECTION TIMES WHERE THEY HAD USEFUL STATISTICAL SIGNIFICANCE. THE DYNAMICAL MODELS SHOW A WIDE RANGE OF TEMPERATURE AND PRECIPITATION PATTERNS FOR NORTH AMERICA - WHICH PROBABLY REFLECTS THE NATURAL VARIABILITY THAT OCCURS IN THE ABSENCE OF ANY STRONG FORCING FROM THE TROPICAL PACIFIC. AS A RESULT THE DYNAMICAL MODEL FORECASTS ARE DE-EMPHASIZED IN THIS SET OF FORECASTS AND WE HAVE REDUCED THE PROBABILITIES AND AREAL COVERAGE OF THE FORECASTS FOR THE U.S. . . . . . . . . PROGNOSTIC DISCUSSION OF OUTLOOKS - SON 2003 TO SON 2004 TEMPERATURE: THE SON TEMPERATURE FORECAST IS BASED PRIMARILY UPON INDICATIONS FROM CCA - OCN AND A COMPOSITE OF PAST CASES FOR THIS SEASON FOR TREND-ADJUSTED ENSO NEUTRAL CONDITIONS. OVER THE CONUS THE TREND REQUIRES POSITIVE ANOMALIES CENTERED OVER THE SOUTHWEST AND FLORIDA - AND IN MANY AREAS THE INDICATIONS FOR WARMTH ARE SUPPORTED BY CCA. EC WAS ASSIGNED IN AREAS WITH CONFLICTS AMONG TOOLS AS WELL AS WHERE THE SIGNALS WERE WEAK OR NON-EXISTENT. FOR ALASKA - THE TOOLS DID NOT GIVE ANY STRONG INDICATIONS FOR ABOVE OR BELOW AVERAGE TEMPERATURE SO EC WAS ASSIGNED TO THE ENTIRE STATE. FROM OND THROUGH MAM TEMPERATURE FORECASTS ARE BASED PRIMARILY UPON COMPOSITES CONDITIONAL UPON ENSO-NEUTRAL CONDITIONS ALONG WITH INDICATIONS FROM CCA AND TREND. WARMER THAN AVERAGE TEMPERATURES ARE PREDICTED IN ALASKA BEGINNING IN NDJ AND LASTING THROUGH SPRING 2004 DUE TO OCN AND EXPECTED WARM OCEANS NEAR ALASKA. OVER THE CONUS - THE CURRENT SET OF FORECASTS EMPHASIZES ONLY THE STRONGEST - MOST CONFIDENT INDICATIONS FROM THAT TOOL. THOSE ARE FOUND MAINLY IN THE SOUTH AND SOUTHWEST DURING WINTER AND IN THE SOUTHWEST IN SPRING AND SUMMER. TRENDS ALONE - AS WELL AS CCA - WOULD FAVOR MUCH OF THE EASTERN HALF OF THE NATION TO HAVE ABOVE NORMAL TEMPERATURES DURING THE WINTER SEASONS - BUT THE ENSO NEUTRAL COMPOSITES AND UNCERTAINTY IN THE AO AND NAO CAUSED US TO PUT EC IN THOSE REGIONS. THE AO AND NAO - WHICH CAN NOT CURRENTLY BE PREDICTED BEYOND A COUPLE OF WEEKS IN ADVANCE - HAVE NOT BEEN AS CONSISTENLTY POSITIVE IN RECENT WINTERS AS THEY WERE IN THE EARLIER PART OF THE PAST DECADE - MAKING MILD WINTERS IN THE NORTHEASTERN THIRD OF THE U.S. LESS OF A SURE THING SINCE THE MID 1990S. FORECASTS BEGINNING WITH AMJ ARE BASED LARGELY ON TREND-ADJUSTED ENSO-NEUTRAL COMPOSITES - OCN AND CCA - WITH INCREASING EMPHASIS ON THE LATTER TWO WITH INCREASING TIME DUE TO GROWING UNCERTAINTY IN THE STATUS OF ENSO AFTER SPRING 2004. THE TREND-ADJUSTED COMPOSITES AND THE TREND ITSELF HAD GOOD AGREEMENT FOR AN AREA OF BELOW NORMAL TEMPERATURES OVER THE HIGH PLAINS BEGINNING IN MAM AND CONTINUING THROUGH MJJ. FORECASTS FOR THE SUMMER 2004 SEASONS INDICATE WARMTH OVER THE SOUTHWEST AND SOUTHEAST FROM OCN WITH SOME SUPPORT FROM CCA. . . . . . . . . PRECIPITATION: ABOVE MEDIAN PRECIPITATION WAS FORECAST FOR SON IN THE SOUTHEAST WHERE INDICATIONS FROM CCA WERE SUPPORTED BY CONSIDERATIONS OF HIGH SOIL MOISTURE AND THE POSSIBILITY OF AN ENHANCED ATLANTIC TROPICAL STORM SEASON. THE INDICATIONS FOR BELOW MEDIAN PRECIPITATION OVER PORTIONS OF THE SOUTHWEST WERE CONSIDERED REASONABLE WITH SUPPORT FROM TREND-ADJUSTED ENSO COMPOSITES AND THUS WERE RETAINED FOR THE FORECASTS THROUGH NDJ - WITH THE AREA OF FORECAST RELATIVE DRYNESS SHRINKING WITH TIME. THE AREA OF ABOVE MEDIAN PRECIPITATION FORECAST FROM NORTHEASTERN TEXAS BEGINNING WITH OND THAT EXPANDS EASTWARD INTO PORTIONS OF THE OHIO AND TENNESSEE VALLEYS DURING DJF WAS INDICATED BY OCN AND THE TREND COMPOSITES FOR ENSO-NEUTRAL CONDITIONS. ANOTHER AREA OF ABOVE MEDIAN PRECIPITATION IS INDICATED BY THE ENSO-NEUTRAL COMPOSITES - AND WEAKLY SUPPORTED BY OCN - FOR THE WESTERN HIGH PLAINS IN FMA. THIS AREA SHIFTS NOTHWESTWARD AND THEN WESTWARD INTO THE PACIFIC NW DURING MAM TO MJJ. NO RELIABLE FORECAST SIGNALS COULD BE SEEN FOR JJA THROUGH SON 2004 - WITH THE EXCEPTION OF DRYNESS IN PORTIONS OF THE FAR WEST DURING JAS INDICATED BY THE TREND-ADJUSTED ENSO-NEUTRAL COMPOSITES WITH SOME SUPPORT FROM OCN AND CCA. FORECAST INDICATIONS FOR PRECIPITATION ARE UNCERTAIN IN MOST OF ALASKA - AND WITH THE EXCEPTION OF STRONGLY-FORCED STABLE COLD-SEASON PATTERNS DURING EL NINO EVENTS - USUALLY HAVE RATHER LOW SKILL - ESPECIALLY IN THE WARM SEASONS. THEREFORE THE ENTIRE STATE WAS LEFT EC FOR PRECIPITATION AT ALL LEADS. NOTE - AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL PROBABILITIES) ARE NOW LABELED EC (EQUAL CHANCES). . . . . . . . . GLOSSARY AND DEFINITIONS: ANALOG (NATURAL ANALOG) - A WEATHER MAP THAT RESEMBLES ANOTHER WEATHER MAP - USUALLY FROM DIFFERENT YEARS BUT THE SAME SEASON IN THE HISTORICAL RECORD. THE CRITERION FOR SELECTING AN ANALOG IS OFTEN THE PATTERN CORRELATION BETWEEN THE MAPS. TWO MAPS WILL JUST BEGIN TO RESEMBLE EACH OTHER TO THE HUMAN EYE AT A PATTERN CORRELATION OF ABOUT 40%. TO BE USEFUL - ANALOGS NEED TO HAVE MUCH HIGHER CORRELATIONS TO THE ORIGINAL MAP THAN THAT - 80% OR MORE. ANALOGS ARE INCREASINGLY DIFFICULT TO FIND AS THE GEOGRAPHIC REGION BEING COMPARED INCREASES IN SIZE. PERFECT ANALOGS TO THE ENTIRE NORTHERN HEMISPHERE SIMPLY DO NOT EXIST - FOR PRACTICAL PURPOSES. THIS IS WHY SIMPLE ANALOG FORECAST METHODS DO NOT WORK VERY WELL. ANNUAL CYCLE - AT MOST LOCATIONS THE CLIMATE STATE VARIABLES - T - P - SST- WIND - AND OTHERS DISPLAY A REGULAR VARIATION WHICH FOLLOWS THAT OF THE ELEVATION OF THE SUN IN THE SKY. A GRAPH OF THE 30 YEAR AVERAGE OF A VARIABLE FOR EACH DAY OF THE YEAR VERSUS DATE SHOWS A WAVE-FORM WHICH - FOR T AT DES MOINES FOR EXAMPLE - RANGES SMOOTHLY FROM LOWEST VALUES IN THE WINTER TO HIGHEST VALUES IN THE SUMMER. ANOMALY - THE ARITHMETIC DIFFERENCE BETWEEN THE VALUE OF A VARIABLE AT A GIVEN PLACE AND TIME AND THE LONG-TERM AVERAGE (USUALLY 30 YEARS) FOR THE LOCATION AND TIME OF YEAR. CA - CONSTRUCTED ANALOG - A LINEAR COMBINATION OF PAST OBSERVED ANOMALY PATTERNS SUCH THAT THE COMBINATION IS AS CLOSE AS DESIRED TO THE INITIAL STATE. A FORECAST IS OBTAINED BY PERSISTING THE WEIGHTS ASSIGNED TO EACH YEAR IN THE HISTORICAL RECORD AND LINEARLY COMBINING THE STATES FOLLOWING THE INITIAL TIME IN THE HISTORICAL YEARS. CAS - CONSTRUCTED ANALOG SOIL MOISTURE PREDICTION TECHNIQUE. CCA - CANONICAL CORRELATION ANALYSIS - A TECHNIQUE WHICH PREDICTS THE STATUS OF U.S. T AND P FOR SOME FUTURE TARGET SEASON USING THE MOST RECENT 4 NON- OVERLAPPING SEASONAL OBSERVATIONS OF TROPICAL PACIFIC SST - CIRCULATION AND U.S. T OR P TO CHARACTERIZE THE RECENT BEHAVIOR OF THE CLIMATE - AND PAST OBSERVATIONS TO PLACE RECENT BEHAVIOR INTO A HISTORICAL CONTEXT. CLIMATOLOGY - THE 30-YEAR AVERAGE OF A VARIABLE - LIKE TEMPERATURE - AT A GIVEN LOCATION AND TIME OF YEAR. . . . . . . . . CONUS - CONTERMINOUS UNITED STATES DYNAMICAL MODEL - A PREDICTION METHOD WHICH USES EQUATIONS DESCRIBING THE PHYSICAL BEHAVIOR OF A SYSTEM AND A COMPREHENSIVE SET OF CURRENT OBSERVATIONS OF THE VALUES OF THE VARIABLES DESCRIBING THE CURRENT STATE OF THE SYSTEM (INITIAL CONDITIONS) TO PREDICT THE VALUES OF THOSE VARIABLES A SHORT TIME-STEP IN THE FUTURE. THOSE VALUES ARE - IN TURN - USED AS THE INITIAL CONDITIONS FOR A SUBSEQUENT PREDICTION - AND SO ON - UNTIL THE DESIRED FUTURE PREDICTION TIME IS REACHED. EASTERLY WIND - WIND BLOWING FROM EAST TO WEST. EC - EQUAL CHANCES - THE PROBABILITY OF THE MOST LIKELY CATEGORY CANNOT BE DETERMINED AND THE EXPECTED LIKELIHOODS OF ABOVE - NORMAL AND BELOW DO NOT DIFFER FROM THEIR CLIMATOLOGICAL ODDS OF 33 1/3% EACH. EC REPLACES CL. EL NINO - THE WARM PHASE OF THE ENSO CYCLE ENSO - ACRONYM FOR EL NINO/SOUTHERN OSCILLATION GCM - GENERAL CIRCULATION MODEL - A GENERIC TERM APPLIED TO GLOBAL DYNAMICAL MODELS. LA NINA - THE COLD PHASE OF THE ENSO CYCLE MJO - MADDEN-JULIAN OSCILLATION - ALSO CALLED TROPICAL INTRA-SEASONAL OSCILLA- TION - A DISTURBANCE IN TROPICAL CONVECTION - PRECIPITATION - WIND AND PRESSURE. MJO PRECIPITATION AND CLOUDINESS ARE ENHANCED ONLY IN REGIONS WHERE SSTS ARE VERY WARM - E.G. INDIAN OCEAN AND WEST PACIFIC. THE PRESSURE AND WIND DISTURBANCE ASSOCIATED WITH MJO IS OBSERVED TO MOVE FROM WEST TO EAST COMPLETELY AROUND THE GLOBAL TROPICS IN ABOUT 30 TO 60 DAYS. NAO - NORTH ATLANTIC OSCILLATION TELECONNECTION PATTERN. NOTE THAT THE STATUS OF THE AO/NAO AND OTHER SLOWLY VARYING CIRCULATION MODES - WHILE VERY IMPORTANT IN DETERMINING THE TEMPERATURE AND PRECIPITATION REGIMES OVER THE US - ARE UNPREDICTABLE BY CURRENT TECHNOLOGY AND ARE NOT EXPLICITLY INCLUDED IN OUR FORECAST PROCESS. NORTHERLY WIND - WIND BLOWING FROM NORTH TO SOUTH. OCN - OPTIMAL CLIMATE NORMALS - A FORECAST BASED ON PERSISTING THE AVERAGE OF THE LAST 10 YEARS FOR TEMPERATURE AND THE LAST 15 YEARS FOR PRECIPITATION. PNA - PACIFIC NORTH AMERICAN TELECONNECTION PATTERN. QBO - QUASI-BIENNIAL OSCILLATION - AN OSCILLATION OF THE WIND IN THE LOWER STRATOSPHERE BETWEEN EASTERLY AND WESTERLY WHICH REVERSES ON A NEARLY- 2 YEAR TIME SCALE. QBO IS ONE OF THE MOST REGULAR OSCILLATIONS KNOWN. SMLR - SCREENING MULTIPLE LINEAR REGRESSION - A TECHNIQUE WHICH SELECTS THE BEST SET OF PREDICTORS - FITTING THEM TO THE OBSERVATIONS TO CREATE EQUATIONS WHICH CAN BE USED TO MAKE PREDICTIONS. SOUTHERLY WIND - WIND BLOWING FROM SOUTH TO NORTH. STATISTICAL PREDICTIONS - PREDICTIONS BASED MAINLY ON LARGE OBSERVATIONAL DATA SETS. CCA - OCN - SMLR - CAS - CA ARE EXAMPLES OF THESE. TELECONNECTIONS - THESE GIVE THE HISTORICAL RELATIONSHIP BETWEEN A GIVEN POINT AND ALL OTHER POINTS OVER A LARGE AREA - LIKE THE NORTHERN HEMISPHERE - FOR A GIVEN TIME OF THE YEAR. THE POINTS ON THE MAP USUALLY CONSIST OF A SET OF MORE OR LESS EVENLY SPACED LOCATIONS CALLED GRID POINTS. TREND - AT A GIVEN LOCATION AND TIME OF YEAR - THE DIFFERENCE BETWEEN THE AVERAGE OF THE MOST RECENT 10 (15) YEARS OF OBSERVATIONS OF T (P) AND THE CLIMATOLOGY. WESTERLY WIND - WIND BLOWING FROM WEST TO EAST. ZONAL FLOW PATTERN - OCCURS WHEN 500-HPA CONTOURS LIE IN AN EAST-WEST DIRECTION PARALLEL TO LATITUDE CIRCLES WITH NEARLY PURE WEST-TO-EAST FLOW. -------------------------------------------------------------------------------- . . . . . . . . FORECASTER: V. E. KOUSKY FOR A DESCRIPTION OF THE STANDARD FORECAST TOOLS - THEIR SKILL - AND THE FORECAST FORMAT PLEASE SEE OUR WEB PAGE AT: HTTP://WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/PREDICTIONS/90DAY/DISC.HTML (USE LOWER CASE LETTERS) INFORMATION ON THE FORMULATION AND SKILL OF THE CAS FORECASTS MAY BE FOUND AT: HTTP://WWW.CPC.NCEP.NOAA.GOV/SOILMST/FORECASTS.HTML (USE LOWER CASE LETTERS) NOTES - THESE CLIMATE OUTLOOKS ARE INTENDED FOR USE PRIOR TO THE START OF THEIR VALID PERIODS. WITHIN ANY GIVEN VALID PERIOD OBSERVATIONS AND SHORT AND MEDIUM RANGE FORECASTS SHOULD BE CONSULTED. THIS SET OF OUTLOOKS WILL BE SUPERSEDED BY THE ISSUANCE OF THE NEW SET NEXT MONTH ON SEP 18 2003. 1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17 2001 FORECAST RELEASE. $$